From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,CP1252 X-Google-Thread: 103376,38c827f7e800d317 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2003-07-03 00:03:44 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!wn14feed!worldnet.att.net!204.127.198.203!attbi_feed3!attbi.com!rwcrnsc52.ops.asp.att.net.POSTED!not-for-mail Message-ID: <3F03D54C.7010008@attbi.com> From: "Robert I. Eachus" User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.0.2) Gecko/20021120 Netscape/7.01 X-Accept-Language: en-us, en MIME-Version: 1.0 Newsgroups: comp.lang.ada Subject: Re: conversion References: <3EFCC18B.4040904@attbi.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit NNTP-Posting-Host: 24.62.164.137 X-Complaints-To: abuse@comcast.net X-Trace: rwcrnsc52.ops.asp.att.net 1057215823 24.62.164.137 (Thu, 03 Jul 2003 07:03:43 GMT) NNTP-Posting-Date: Thu, 03 Jul 2003 07:03:43 GMT Organization: Comcast Online Date: Thu, 03 Jul 2003 07:03:43 GMT Xref: archiver1.google.com comp.lang.ada:40004 Date: 2003-07-03T07:03:43+00:00 List-Id: Dmitry A. Kazakov wrote: > If you mean that unversal integer is something like String, then you > are probably right. But the difference is that we cannot declare > objects of universal integer. On contrary, for strings we can, but > surprisingly that type is called "Unbounded_String" and even more > surprising is that it is unrelated to String. No! No! No! You are very confused. First of all, what do you think the type of Foo is in: Foo: constant := 123456789012; (Actually in Ada 95 it is _root_integer_ while the literal 123456789012 is of type _universal_integer_, but that is a detail. (_root_integer_ includes all other integer types, including _universal_integer_.) The Integer type that corresponds most closely to String, is Integer, and they are both declared in Standard. > It is clear (isn't it) that all different string types have same > semantics and differ only in how they implement that semantics. So > they should be related. Yes, so the three different implementations are all clustered under Ada.Strings: Ada.Strings.Fixed, Ada.Strings.Bounded, and Ada.Strings.Unbounded. > That length of a String value cannot be > changed is just a value constraint which by no means changes string > semantics. No. String values are never constrained, String objects are always constrained, often by their initial values. If I have a function that may return a different length string every time it is called, and that length is unpredictable in advance? That is not a problem, it is a common idiom: while not Done loop declare Buffer: String := Get_Line; begin -- process Buffer... end; end loop; There is no static/dynamic dichotomy here, nor is there a bounded/unbounded distinction, or even constrained/unconstrained. Buffer is always constrained to be the same length as the String returned by the most recent call to Get_Line. (Unfortunately that function is not Ada.Text_IO.Get_Line, but I hope we will fix that next time around.) > So instead of looking for explanations which I doubt would convince > anybody, one could simply admit that, yes, String and Unbounded_String > should be better siblings, but to do it consistently would require too > many changes Ada's ADT model. Ada.Strings.Fixed, Ada.Strings.Bounded, and Ada.Strings.Unbounded are the siblings. It may bother you that Ada.Strings.Fixed reuses String, and Ada.Strings.Bounded is a generic package you have to instantiate, but those are not the issues you are describing here. > For example, what would happen if > > type Name is new Unbounded_String; > > Should it produce a new String type? Surely. How should it be named? > Who knows. It would be named Name, unless I am missing something, just as: type New_String is new String; Creates a new string type named New_String. Or if you prefer: type New_String is array(Positive range <>) of Character; pragma Pack(String); Do that in Ada and you will find that you get a type with literals like "foo"... String is not a priviledged type in Ada. You can even create a new character type--Character is similarly not special. For example you could create a Cyrillic character type which used ISO 8859/5 Latin/Cyrillic with the upper and lower pages reversed. Or whatever. A character type is an enumeration type with character literals. A string type is any array of any character type. -- Robert I. Eachus �In an ally, considerations of house, clan, planet, race are insignificant beside two prime questions, which are: 1. Can he shoot? 2. Will he aim at your enemy?� -- from the Laiden novels by Sharon Lee and Steve Miller.